1. Field of the Invention
The present invention relates to a vertical probe card, and in particular, to a technique covering circuit design, structural arrangement and assembly regarding the vertical probe card.
2. Description of the Prior Art
Generally, wafer testing can be carried out using a vertical probe card. Its essential procedure is bonding the IC test substrate with a Probe PCB by soldering before test, and the test is performed after the packaging process because the bandwidth is limited for the vertical probe card. Result of test made as such causes low yield of packaging and high of production cost as well.
FIG. 1 is a schematic view of a conventional vertical probe card for integrated circuit (IC). As shown in FIG. 1, the vertical probe card 100 for IC comprises an IC test substrate 110 and a probe PCB 120 as two components. The way of general signal (including source signal) transmission is transmitting a signal 131 at the device under test (DUT) terminal to the direction of the test side by a probe contacting C4 pad 111. After passing a metal conductor 112 in the IC test substrate 110, the signal is transmitted to the probe PCB 120 by way of connecting the BGA pad 113 with a solder ball 140, then to a through hole 122, a metal conductor 123, another through hole 122 to a pogo pad 124 on the other surface. In this way the signal is transmitted into the test side to be deciphered. A high frequency signal 130 is also transmitted in this manner, but for avoiding a larger loss in the transferring interface, the signal is inputted into the test side through a connector 150.
Such a serial transmission passage is apt to be affected by the PCB of different materials and structural deference (for example: line width of trace, clearance, via size and depth of the through holes etc.). The above factors cause unmatching and discontinuity of impedance leading to return loss due to insertion loss and reflection. Such a phenomenon is more significant to the high frequency signal. For facilitating the signal to pass the through holes, it is necessary enlarge the cross sectional area of the through holes. Presently it can not be realized for the BGA package because its spacing is narrow. As the power source and signals take the same route, the area of the power line in the horizontal direction can be widened as broad as possible so as to carry the current with reduced inductance. But transmission in the vertical direction is limited by the diameter of the through holes. The inductance is increased, and will give rise to a simultaneous switch noise (SSN) and an excessive source target impedance.
Accordingly, the idea of improvement is directed to maintaining perfection of the signal transmission, this can be achieved through reconstruction of the passage and the scheme of the signal transmission so as to reduce on route loss of the signal transmission. By connecting the selectively cooperative transmission elements, the insertion loss problem can also be effectively improved. Besides, the reform of power source may contribute to improving manner and scheme of the signal transmission in the vertical direction. Combination of circuit design, production scheme and process through repeated experimentation, research and investigation will result in achieving integrity of power source and signals.